In the field of the magnetic disc, a 2 MB MF-2HD floppy disc using Co-modified iron oxide has been generally loaded in a personal computer. However, along with the rapid increase in the amount of data to be dealt with, the capacity of the disc has become insufficient and the increase in the capacity of the floppy disc has been demanded.
Magnetic recording media comprising a magnetic layer containing an iron oxide, a Co-modified iron oxide, CrO2, ferromagnetic metal powder, or hexagonal ferrite powder dispersed in a binder coated on a nonmagnetic support have been conventionally widely used. Ferromagnetic hexagonal ferrite fine powders have been known to have excellent high density recording characteristics among these.
On the other hand, a disc-like magnetic recording medium (magnetic recording medium in the form of a disk) comprising a thin magnetic layer and a functional nonmagnetic layer has been developed and floppy discs of the class with the capacity of 100 MB are now on the market. As floppy discs showing these characteristics, the constitution comprising a magnetic layer having Hc of 1,400 Oe or more and a thickness of 0.5 μm or less and a nonmagnetic layer containing electrically conductive particles is proposed in JP-A-5-109061 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”).
However, with the rapid trend of the increase in the capacity and density of magnetic disc media, it has become difficult to obtain satisfactory characteristics even with these techniques. In particular, when high recording density is actualized, the smoothest possible surface is necessary for obtaining high electromagnetic characteristics.
A magnetic disc medium is generally designed so that the surface of the magnetic sheet is maintained clean by means of a liner (see JP-A-5-20832).
When hexagonal ferrite powder is used in a magnetic disc medium, however, a recording layer is scraped off due to the liner, and the resulting minute recording layer defects and the minute dusts of the liner flocks cause dropout, which suddenly increases an error rate. Patent literature 2 aims at preventing the mold growing in a magnetic disc medium and the above problem is not disclosed.
Accordingly, it has been desired to develop a liner material suitable for a magnetic layer containing a hexagonal ferrite powder and excellent in surface smoothness, which can ensure the surface property and the surface cleanliness of the magnetic layer and can get rid of the scraping of the liner, to thereby provide a magnetic disc medium free of dropout.